Preformed workpieces such as decorative mouldings are widely used in the construction industry. Such mouldings are designed to be mounted against exterior or interior walls for providing architectural features on building structures in sectors such as residential, industrial, communercial and institutional buildings. The exposed surface of the moulding is usually decorative and as such, has an irregular surface in cross-section and continuous in the longitudinal direction. Mouldings can be fabricated from several materials including wood, plaster and expanded polystyrene (EPS). EPS mouldings are particularly attractive to use because of their relatively light weight and ease of fabrication. In order that the moulding be both attractive and durable, moulding substrates or workpieces are typically coated with various coating materials to provide an attractive finish to the product. Traditionally, mouldings have been coated by band after the EPS moulding is secured to the exterior of the structure. This involved applying with hand tools, a layer of base coat to the moulding and then embedding a fiberglass mesh onto the moulding and allowing it to dry. A layer of stucco or special paint as a finish coat is then finally applied to the base coated moulding. This method is very labor intensive and consequently, very slow and expensive. Often times, the quality of the applied coating is not consistent due to poor workmanship. This results in a coating of uneven thickness which eventually cracks and does not look very attractive.
More recently, various types of automated equipment have been designed to apply coatings to different types of workpieces. For example, U.S. Pat. No. 5,514,417 discloses a method and apparatus for coating a molded fibrous, workpiece with a foam material. In this method and apparatus, the workpiece is passed through a foam bath within a coating chamber. To ensure a good coating of the workpiece, the foam material is spread over the entire exterior surface of the workpiece using wipers within the coating bath.
Canadian patent application 2,184,205 discloses a method and apparatus for providing a coating material onto the surface of a workpiece. In this method, the workpiece is passed through a bath of coating material contained within a coating chamber for applying under weight of the material, a coating. The workpiece is advanced on a platform by a set of guide rollers abutting both sides of the workpiece both before and after passing through the coating bath. While this method and apparatus does provide a coating on the decorative surface of the workpiece, the resultant coating may be inconsistent with respect to its thickness. This is partly due to the fact that the workpiece moves about on the platform as it is being guided into the coating chamber. This is also true when the workpiece exits the coating bath, as lateral, horizontal and vertical movement will result in varying thicknesses of coating material being applied to the surface of the workpiece as it exits the coating bath, Furthermore, once in the coating chamber, the coating material under gravity may not evenly distribute into the intricate curves present on the exterior design of the workpiece. The coating material can bubble on the surface of the workpiece due to having the workpiece pass through a bath of thick, viscous coating material at varying speeds which results in different rates of shear of the material at the bath exit. Consequently, parts of the workpiece will not be coated adequately or not at all. Once the workpiece exits the bath, it is not allowed to dry sufficiently before the guide rollers, continue to advance it forward and thus contact the wet coated workpiece and possibly damage its coating. Also, it is required that the coated mouldings air dry for at least 24 hours.
There is therefore a need to develop a novel method and apparatus for coating decorative workpieces used widely in various construction sectors, in a consistent, simple, efficient manner such to provide a smooth coating distributed in a controlled manner over the entire exposed decorative surface of a workpiece.